The present invention relates to an improvement of a cage constructing a rolling bearing which is used in rotating machines of various types such as a magnetic disk device, an optical disk device, a laser printer, a video tape recorder, a machine tool and a general machine. In the cage for a rolling bearing of the invention, lubrication of sliding contact portions between the cage and rolling elements is sufficiently ensured so that vibrations and noises of the rolling bearing are lowered.
A ball bearing such as shown in FIG. 24 is widely used as a rolling bearing for supporting a variety of rotating portions in rotating machines of various types. In a ball bearing, an inner race 2 having an inner raceway 1 on the outer peripheral face, and an outer race 4 having an outer raceway 3 on the inner peripheral face are concentrically disposed, and a plurality of balls 5 are rollingly arranged between the inner raceway 1 and the outer raceway 3. In the illustrated example, both the inner raceway 1 and the outer raceway 3 are of the deep groove type. The plurality of balls 5 are rollingly held in pockets 8 formed in a cage 6.
The cage 6 which constructs the ball bearing shown in FIG. 24 is the one which is called a corrugated press cage, and combines a pair of elements 9 which are corrugated and formed into an annular shape. Each element is formed by pressing a metal plate member. In the elements 9, substantially semicircular recesses 8a for forming the pockets 8 are formed at plural positions arranged in the circumferential direction. The portions of the pair of elements 9 other than the recesses 8a are butted each other and securely bonded together by a plurality of rivets 10, thereby forming the cage 6 which has an annular shape and forms the pockets 8 at plural positions arranged in the circumferential direction. The middle portion of the inner face of each recess 8a is formed as a holding recessed face 11 having an arcuate section shape and a radius of curvature which is slightly larger than that of the outer face of each ball 5. When the pair of elements 9 are abutted against each other, the recesses 6a are combined with each other and the pockets 8 are formed. A holding recess face 11 is formed as a holding face in the middle portion of each of the pockets 8. The holding recess face 11 has a radius of curvature which is slightly larger than that of the rolling face of each ball 5.
FIG. 25 shows a cage 6a which is called a crown-type cage. In the cage, pockets 8 which rollingly hold the balls 5 (FIG. 24) are formed at plural positions arranged in the circumferential direction of an annular main portion 7 made of a synthetic resin or the like. In the cage 6a of the crown type, each pocket 8 includes: opposing side faces of a pair of elastic pieces 12 which are disposed on the main portion 7 with being separated from each other; and a spherical recessed face 20 which is a part of one face (the upper face in FIG. 24) in the axial direction (the vertical direction in FIG. 24) of the main portion 7 and which is between the pair of elastic pieces 12. The radius of each curvature of the recessed face 20 and the opposing side faces of the elastic pieces 12 is slightly larger than that of the outer face of the ball 5. The opposing side faces of the elastic pieces 12, and the recessed face 20 form a holding recessed face.
When the ball bearing is to be assembled, each ball 5 is pressingly inserted between the pair of elastic pieces 12 forming the pocket 8, while elastically widening the clearance between the front end edges of the elastic pieces 12. In this way, the cage 6a embraces the balls 5 in the pockets 8, so that the balls 5 are rollingly held between the inner raceway 1 and the outer raceway 3 (FIG. 24).
In the use of a ball bearing comprising the cage 6 or 6a, the inner race 2 and the outer race 4 are made relatively rotatable as the plural balls 5 roll. At this time, the balls 5 revolve around the inner race 2 while rotating. The cage 6 or 6a rotates around the inner race 2 at the same speed as the revolution speed of the balls 5.
A lubricant, for example, lubricating oil such as grease is filled or continuously supplied into a space between the outer peripheral face of the inner race 2 and the inner peripheral face of the outer race 4 so that the relative rotation is smoothly performed. This prevents the ball bearing from generating vibrations and noises, and failures such as seizure from occurring. In some types of ball bearings, both end openings of the space between the outer peripheral face of the inner race 2 and the inner peripheral face of the outer race 4 are closed by a sealing member such as a seal plate or a shield plate, thereby preventing the lubricant from leaking from the space or foreign substances such at dust from entering the space. FIG. 24 shows the ball bearing which is not provided with such a sealing member.
In a ball bearing into which the cage 6 or 6a is incorporated, even when a required amount of a lubricant is filled or supplied, there arises a case where vibrations are induced in the cage 6 or 6a and noises called a cage sound or vibrations are generated in the ball bearing into which the cage 6 or 6a is incorporated. Such vibrations of the cage 6 or 6a are caused by large motion of the cage 6 or 6a with respect to the balls 5, and on the basis of sliding friction between the balls 5 which are rolling elements, and the cage 6 or 6a. In order to suppress generation of such a cage sound, conventionally, the clearance between the inner face of each pocket 8 and the rolling surface of the ball 5 is reduced in size so that the amount of motion of the cage 6 or 6a with respect to the balls 5 is reduced, thereby suppressing generation of a cage sound.
When only the amount of motion of the cage 6 or 6a with respect to the balls 5 is reduced, however, a cage sound is generated owing to the shape of the inner peripheral faces of the pockets 8 of the cage 6 or 6a. The reason of this phenomenon will be described with reference to FIGS. 26, 27, and 8B. FIGS. 8A and 8B show differences in structure between the invention and the conventional example. FIG. 8B shows the conventional structure. As shown in FIGS. 26, 27, and 8B, sharp (large curvature) edges 13 exist in opening peripheral portions 17 or 19 of the pockets 8 of the cage 6 or 6a. The edges 13 function as a resistance to the flow of a lubricant. In short, in both the corrugated cage 6 which is produced by pressing a metal plate member and the crown-type cage 6a which is produced by injection molding of a synthetic resin, sharp edges due to burrs exist in opening peripheral portions of the pockets 8, and hence the edges 15 have a very large curvature.
When the clearance between the inner face of each pocket 8 and the rolling surface of the ball 5 is reduced in size in order to suppress a cage sound, a lubricant hardly enters a clearance 14 between the rolling surface of the ball 5 and the holding recessed face 11 (in the case of the cage 6 shown in FIGS. 26 and 8B; in the case of the cage 6a shown in FIG. 27, the recessed face 20 functioning as a holding recessed face). Also edges 15 exist in the peripheral portion of the holding recessed face 11 indicated by a one-dot chain line in FIG. 8B. Accordingly, a lubricant is caused by the rolling of the ball 5 to proceed from the peripheral space to the clearance 14. Consequently, a lubricant which overrides the edges 13 so as to enter the pocket 8 is scraped off by the edges 15, so that the lubricant is caused to hardly enter the clearance 14 in an inner portion of the pocket 8. Therefore, a sufficient amount of the lubricant cannot enter the clearance 14 between the holding recessed face 11 and the rolling surface of the ball 5, with the result that frictional vibration occurring in the sliding contact portions between the cage 6 or 6a and the balls 5 cannot be sufficiently suppressed and vibrations and noises are induced.
Further, when only the amount of motion of the cage 6 or 6a with respect to the ball 5 is reduced, a cage sound may be generated owing to the shape of the inner peripheral face of the pockets 8 of the cage 6 or 6a, under severe operation conditions such as the case where lubrication is insufficiently conducted. Specifically, in the conventional cages 6 and 6a shown in FIGS. 24 and 25, the inner peripheral face of the pocket 8 can be slidingly contacted in its substantially entire width with the rolling surface of the ball 5, and hence the friction force acting between the inner peripheral face and the rolling surface is increased. This phenomenon will be described in detail with reference to FIGS. 28 to 31.
The first example of the conventional structure shown in FIG. 24 will be described. In the inner peripheral face of the pocket 8, as indicated by crosshatching in FIGS. 28 and 29, most of the area of the recess 8a functions over the entire width as a holding and guiding face having a radius of curvature which is slightly larger than that of the rolling surface of the ball 5 (FIG. 24). Also in the case of the second example of the structure indicated by crosshatching in FIGS. 30 and 31, the inner peripheral face of the pocket 8 functions over the entire width as a holding and guiding face having a radius of curvature which is slightly larger than that of the rolling surface of the ball 5.
When the inner peripheral face of the pocket 8 functions over the entire width as a holding and guiding face as described above, the frictional area between the inner peripheral face of the pocket 8 and the rolling surface of the ball is widened. This increases frictional vibration occurring in the sliding contact portions between the cage 6 or 6a and the balls 5, thereby inducing vibrations and noises.